Structure containing metal microparticles

ABSTRACT

The present invention addresses the problem of providing a structure which comprises metal plate microparticles and a lipophilic clay-based intercalation compound and which exhibits excellent stability. The problem is solved by a structure as described above wherein: the metal plate microparticles are platy microparticles alone or a mixture thereof with polyhedral microparticles (including spherical microparticles); the platy microparticles have a thickness of 1 to 50 nm, a length of principal plate of 10 to 5000 nm and an aspect ratio thereof of 3 or more; and the weight ratio of the lipophilic clay-based intercalation compound to the metal plate microparticles is 0.01 to 50.

TECHNICAL FIELD

The present invention relates to a structure comprising metalmicroparticles and a specific lipophilic montmorillonite mineral groupor mica mineral group.

BACKGROUND ART

Until now, various compositions containing metal microparticles thatexploit the characteristics of fine metal particles have been proposed.For example, Patent Document 1 describes that precious metalmicroparticles are allowed to agglomerate in a flowable matrix asrepresented by smectite to obtain a composite having a stableagglomeration state.

Now, since the surface and the interlayer space of a montmorillonitemineral group (clay-based layered compound) such as smectite arehydrophilic, it has properties of showing affinity with a highly polarsolvent such as water or dimethylsulfonamide but not with a solventhaving low polarity such as toluene or ketonic solvent. Therefore, useof a montmorillonite mineral group such as smectite has been difficultto produce a composite of metal particles and a layered compound thathas affinity with a substance having low polarity. Meanwhile, acomposite of metal particles and a layered compound that has affinitywith a substance with low polarity has industrial benefits such as: (1)good working efficiency due to good volatility; and (2) enhancement of aphotoelectric conversion efficiency of an organic solar cell.

The present inventor had succeeded in accomplishing an invention of amethod for producing a composite of metal particles and a layeredcompound which has good affinity with a substance having low polarity byintercalation of organic ions (Patent Document 2). This method, however,has problems such as: (1) use of metal particles (metal platemicroparticles, etc.) other than metal colloids (metal particles, ormetal particles whose surface is at least partially covered with adispersant such as citric acid); and (2) further enhancement of thedispersion stability for practical use.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2006-184247

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2012-166145

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention has an objective in obtaining a structurecomprising metal plate microparticles and a lipophilic clay-basedintercalation compound, which is excellent in dispersion stability andhas practical stability.

Means for Solving the Problems

In order to solve the above-described problems, the present inventorshave continued studies on a dispersion stabilizer for metal platemicroparticles and consequently found that a structure which isexcellent in dispersion stability and has practical stability can beobtained by mixing metal microparticles with a specific clay-basedintercalation compound at a specific mixing ratio, thereby accomplishingthe present invention. Examples of the shapes of the metalmicroparticles include a sphere, a cube, a cuboid, polyhedrons such asan octahedron, a star, a plate, a rod, a wire and a prism. Inparticular, the metal particles have a plate-like shape alone, or amixture of a sphere, a cube, a cuboid or a polyhedron such as anoctahedron and a plate-like shape so that the structure of the presentinvention shows various properties by controlling the ratio thereof.

Specifically, the present invention is a structure containing metalmicroparticles and a lipophilic clay-based intercalation compound at aweight ratio of 0.01 to 50. The metal microparticles are, for example,at least one selected from the group consisting of gold, silver, copper,platinum, palladium and rhodium. In addition, according to the presentinvention, at least some of the metal microparticles have plate-likeshapes, where the plate-like metal microparticles have a thickness of 1nm to 50 nm and the long axis of the principal plane of 10 nm to 5000nm. Moreover, the aspect ratio of the plate-like metal microparticles isat least 3, and preferably 3 or more. Herein, an example of the metalmicroparticles contains at least silver.

Furthermore, a lipophilic clay-based intercalation compound belongs to alipophilic montmorillonite mineral group or a mica mineral group. In apreferred embodiment, while the lipophilic clay-based intercalationcompound is lipophilic smectite, lipophilic saponite or lipophilichectorite, a synthetic compound may also be used as the lipophilicclay-based intercalation compound. The structure of the presentinvention is preferably a film-like structure.

In addition, the present invention is a method for producing a structurecontaining metal microparticles and a lipophilic clay-basedintercalation compound at a weight ratio of 0.01 to 50, the methodcomprising Steps 1 to 3 below.

Step 1: step of preparing a dispersion solution containing metalmicroparticles, a clay-based intercalation compound and a liquiddispersion medium such that the weight ratio of the metal microparticlesand the lipophilic clay-based intercalation compound is 0.01 to 50.

Step 2: step of coating the dispersion solution on a support to obtain acoated film.

Step 3: step of removing the liquid dispersion medium from the coatedfilm.

In Step 1, the dispersion solution preferably contains a resin. Examplesof the resin include at least one type selected from the groupconsisting of polyol, polycarboxylic acid, polysulfonic acid, polyether,polyester, polyamide, polyvinyl butyral, polysiloxane, polyvinylpyrrolidone and polycation compounds.

Furthermore, the present invention is a structure containing polyhedronmetal microparticles including spherical microparticles with an averageparticle size of 1 nm to 300 nm, plate-like metal microparticles with athickness of 1 nm to 50 nm, a long axis of the principal plane of 10 nmto 5000 nm and an aspect ratio is 3 or more, and a lipophilic clay-basedintercalation compound.

Effect of the Invention

According to the present invention, a structure having a practicalstrength can be obtained while maintaining the dispersion stability ofthe metal microparticles as much as possible. Furthermore, according tothe present invention, a structure having a practical strength and thatcan easily absorb light by increasing the plasmon effect, a structurehaving a practical strength with increased transparency for visiblelight, and a structure having a practical strength with increasedsubstance permeability can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A picture of a structure according to a first embodiment of thepresent invention taken with a scanning electron microscope.

FIG. 2 A picture of a structure according to a third embodiment of thepresent invention taken with a scanning electron microscope.

FIG. 3 A picture of a structure according to a fourth embodiment of thepresent invention taken with a scanning electron microscope.

FIG. 4 A picture of the plate-like silver nanoparticle A aqueousdispersion (dried product) prepared in Example 2 taken with a scanningelectron microscope.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, modes for carrying out the present invention will bedescribed in detail.

A first embodiment of the present invention is a structure containingmetal microparticles and a lipophilic clay-based intercalation compoundat a weight ratio of 0.01 to 50.

Metal microparticles of a structure according to a second embodiment ofthe present invention consists of at least one selected from the groupconsisting of gold, silver, copper, platinum, palladium and rhodium.

Metal microparticles of a structure according to a third embodiment ofthe present invention have a plate-like shape, where the plate-likemetal microparticles have a thickness of 1 nm to 50 nm, a long axis ofthe principal plane of 10 nm to 5000 nm, and an aspect ratio of 3 ormore. In addition, another embodiment of a structure of the presentinvention contains plate-like metal microparticles alone, or a mixtureof polyhedron metal microparticles including spherical microparticleswith an average particle size of 1 nm to 300 nm and plate-like metalmicroparticles, where the weight ratio of the polyhedron microparticlesincluding spherical microparticles is 10 or less with respect to theplate-like metal microparticles.

A structure according to a fourth embodiment of the present invention isa clay-based intercalation compound that is lipophilic. A structureaccording to another embodiment of the present invention has metalmicroparticles with a plate-like shape, where the thickness of saidplate-like microparticles is 1 nm to 50 nm, the long axis of theprincipal plane of 10 nm to 5000 nm and the aspect ratio of 3 or more.The structure contains the plate-like microparticles alone or a mixtureof it with polyhedron metal microparticles including sphericalmicroparticles with an average particle size of 1 nm to 300 nm, and alipophilic clay-based intercalation compound. The lipophilic clay-basedintercalation compound may of a single type or a combination of multipletypes of clay-based intercalation compounds.

The clay-based intercalation compounds of the present invention refer toa montmorillonite mineral group and a mica mineral group. Themontmorillonite mineral group is a clay mineral represented by thefollowing general formula (X,Y)₂₋₃Z₄O₁₀(OH)₂.mH₂O—(W_(1/3)) [wherein,X=Al, Fe(III), Mn(III), Cn(III); Y=Mg, Fe(II), Mn(II), Ni, Zn, Li; Z=Si,Al; W=K, Na, Ca; H₂O is interlayer water; and m is an integer]. Here,depending on the difference in the combination as well as the number ofsubstitution of X and Y, there may exist many types of natural productssuch as montmorillonite, magnesian montmorillonite, ironmontmorillonite, iron magnesian montmorillonite, beidellite, aluminianbeidellite, nontronite, aluminian nontronite, saponite, aluminiansaponite, hectorite and sauconite. Other than these natural products,synthetic compounds and the like in which the OH group in theabove-mentioned general formula is replaced by a halogen such asfluorine are also commercially available and any of them can be used.

The mica mineral group may be sodium silicic mica, sodium taeniolite orlithium taeniolite. In particular, a lipophilic clay-based intercalationcompound that can be synthesized from a clay-based intercalationcompound and C₄-C₂₀ alkyl quaternary ammonium cation is useful for thepresent invention. Examples include smectite such as Lucentite SAN,Lucentite SAN316, Lucentite STN, Lucentite SEN and Lucentite SPN (alltrade names) from Co-op Chemical Co., Ltd., saponite (e.g., organifiedsaponite) and bentonite from Kunimine Industries Co., Ltd., andhectorite (e.g., organified substance of synthetic hectorite) fromRockwood.

The average particle sizes of the polyhedron metal microparticlesincluding spherical microparticles and the plate-like metalmicroparticles used with the present invention are measured by dynamiclight scattering method, Sears method, laser diffraction/scatteringmethod or the like. The aspect ratio of the plate-like metalmicroparticles is determined from an image observed using a scanningelectron microscope.

Hereinafter, the first embodiment of the present invention will bedescribed.

The first embodiment of the present invention is a structure in which aweight ratio of the metal microparticles and the lipophilic syntheticsmectite (weight of lipophilic synthetic smectite/weight of metalmicroparticles) meets 0.01 to 50. The structure of the present inventionmay take a form of an aggregate which is formed such that the surfacesof the plate-like metal microparticles and the polyhedron metalmicroparticles including spherical microparticles are covered bysmectite. Accordingly, a structure excellent in dispersion stability andalso excellent in temporal stability can be obtained.

A microscopic picture of the structure according to the first embodimentthe present invention taken with a scanning electron microscope is shownin FIG. 1. In this structure, the plate-like metal microparticles arecovered with smectite, and they hardly agglomerate with other plate-likemetal microparticles. In the above-described state, the structureexhibits special optical property due to the surface plasmon effect ofthe plate-like metal microparticles, and expresses a light absorbingeffect. In this regard, it may be preferable, depending on the desiredoptical property, that the principal planes of about 2 to 5 plate-likemetal microparticles are assembled/agglomerated with each other, andthus it is important to strictly control the agglomeration state of theplate-like metal microparticles upon producing the structure of thepresent invention.

According to the first embodiment of the present invention, the weightratio of the metal microparticles and the lipophilic synthetic smectite(weight of lipophilic synthetic smectite/weight of metal microparticles)meets 0.01 to 50. If this weight ratio is less than 0.01, the dispersionstability would be insufficient and results in poor temporal stability.On the other hand, if the weight ratio is 50 or higher, the amount ofsmectite covering the plate-like metal microparticles and else becomestoo much, resulting in low surface plasmon effect. In particular, theweight ratio is preferably 0.05 to 20 for the purpose of effectivelyexpressing various optical properties of the plate-like metalmicroparticles.

The metal microparticles are plate-like microparticles alone or amixture of polyhedron microparticles including spherical microparticlesand plate-like microparticles. The plate-like metal microparticles havea thickness of 1 nm to 50 nm and a principal plane with a shape of astar, a triangle, a polygon, a substantial polygon or the like, wherethe long axis of said principal plane is 10 nm to 5000 nm and the aspectratio thereof is 3 or more. In terms of interaction force between theplates such as the interactomic force and the van der Waals' force, thelong axis of the plate-like metal microparticles is preferably 30 nm to1500 nm.

The aspect ratio according to the present invention is the valueobtained by dividing the long side of the principal plane by thethickness. Here, the plate-shaped principal plane has the largest areaand refers to two planes facing each other, while the thickness refersto the side length sandwiched in between the two principal planes.Additionally, the shape of a star or a polygon of the principal planerefers to the shape of the principal plane projected in the normaldirection. The long side of the principal plane refers to the longestpart between a corner (apex) to a corner (apex) of the principal plane.

Hereinafter, the second embodiment of the present invention will bedescribed.

While the structure according to the second embodiment of the presentinvention contains at least one of gold, silver, copper, platinum,palladium and rhodium as the metal microparticles, it preferablycontains a single composition of any one of gold, silver or copper or analloy containing at least one of them, and particularly preferablycontains silver alone.

Hereinafter, the third embodiment the present invention will bedescribed.

The third embodiment of the present invention is a structure thatcontains metal plate microparticles alone, or polyhedron metalmicroparticles including spherical microparticles having an averageparticle size of 1 nm to 300 nm and plate-like metal microparticleshaving a thickness of 1 nm to 50 nm, the long axis of the principalplane thereof of 10 nm to 5000 nm and the aspect ratio thereof of 3 ormore, where the weight ratio of the metal microparticles is 10 or lesswith respect to the plate-like metal microparticles. Although the mixedamount of the polyhedron metal microparticles including the sphericalmicroparticles may preferably be as small as possible for some cases,their existence is inevitable to some extent through the productionsteps or due to the fracture of the plate. According to the presentinvention, depending on the desired optical properties (for example,light-scattering property or the like), it may be more preferable thatthe polyhedron metal microparticles including spherical microparticlesand the plate-like metal microparticles are mixed together for somecases, in which cases it is important to control the above-describedweight ratio.

A picture of the structure according to the third embodiment of thepresent invention taken with a scanning electron microscope is shown inFIG. 2. FIG. 2 shows the spherical metal microparticles attached to theplate-like metal microparticles, where both microparticles are coveredwith smectite.

Hereinafter, the fourth embodiment of the present invention will bedescribed.

The fourth embodiment of the present invention is a structure in whichthe smectite is a lipophilic synthetic smectite. A picture of thestructure according to the fourth embodiment of the present inventiontaken with a scanning electron microscope is shown in FIG. 3. Thelipophilic synthetic smectite can be finely dispersed or molecularlydissolved in a solvent to cover the metal microparticles and else. Sincethe metal microparticles and else can easily be dispersed in thesolvent, it can be easily applied to a structure of the presentinvention and the formation of the film thereof becomes easy.

The structure of the present invention is made of a composite in whichthe surfaces of the metal microparticles are coated with a lipophilicclay-based intercalation compound. Another embodiment of a structure ofthe present invention may also take a form in which the metalmicroparticles are assembled or agglomerated in the above-describedcomposite. Another embodiment of a structure of the present inventionmay alternatively take a layered form in which the metal microparticlesare laminated in the above-described composite. According to anotherembodiment of a structure of the present invention, the above-describedcomposite may also be used in a mixture, an assembly or a compositiondepending on use.

Although the structure of the present invention may have a film-likeshape, a fiber-like shape, a particle-like shape or the like, afilm-like shape is preferable from the perspective of the beneficial useof the expressed optical property, substance permeability, conductivityand else. In this case, in order to maintain the flexibility of thefilm, the thickness of the structure is preferably 10 μm or less.

Hereinafter, a method for producing a structure of the present inventionwill be described by taking a structure in a film-like form as anexample. The structure of the present invention can efficiently beproduced by utilizing a liquid dispersion medium (Steps 1 to 3).

Step 1: Step of preparing a dispersion solution containing metalmicroparticles, a lipophilic clay-based intercalation compound and aliquid dispersion medium such that the weight ratio of the metalmicroparticles and the lipophilic clay-based intercalation compound is0.01 to 50.

Step 2: Step of coating the dispersion solution onto a support to obtaina coated film.

Step 3: Step of removing the liquid dispersion medium from the coatedfilm.

Typically, the dispersion solution used with the present invention maybe prepared, for example, according to any one of the following methods[1] to [4], although the method for preparing the dispersion solution isnot limited these methods.

[1] Method in which metal microparticles and a lipophilic clay-basedintercalation compound used are all added to and dispersed in a commonliquid dispersion medium at the same time.

[2] Method in which metal microparticles are dispersed in a liquiddispersion medium to prepare a metal microparticle dispersion solutionwhile a lipophilic clay-based intercalation compound is dispersed in aliquid dispersion medium to separately prepare a lipophilic clay-basedintercalation compound, and subsequently the respective dispersionsolutions are mixed.

[3] Method in which metal microparticles are dispersed in a liquiddispersion medium to prepare a metal microparticle dispersion solution,to which a lipophilic clay-based intercalation compound is added anddispersed therein.

[4] Method in which metal microparticles are formed in a liquiddispersion medium to prepare a metal microparticle dispersion solutioncontaining the metal microparticles while a lipophilic clay-basedintercalation compound dispersion solution containing a lipophilicclay-based intercalation compound is separately prepared, andsubsequently the respective dispersion solutions are mixed.

In order to achieve more homogeneous dispersion, the dispersion solutionis subjected to forced dispersion procedure such as ultrasonicdispersion, ultrahigh-pressure dispersion or the like, therebyhomogeneously dispersing the metal microparticles in the dispersionsolution. In addition, the lipophilic clay-based intercalation compoundand the metal microparticles used for preparing the dispersion solutionare preferably in colloid states.

The liquid dispersion medium of the present invention may be any mediumas long as it has the function to allow dispersion of the metalmicroparticles and else. Water or an organic solvent may be used.Moreover, the metal microparticles may be subjected to surface treatmentin order to improve the dispersibility in the above-described solvent,or may be added with a dispersion medium electrolyte or a dispersantassistant.

If the metal plate microparticles and smectite are to be dispersed incolloidal states in Step 1 mentioned above, pH may be adjusted, or anelectrolyte, in particular citric acid or other similar organic acid anda dispersant may be added, as necessary. Furthermore, for homogeneousdispersion, a procedure such as stirring with a stirrer, ultrasonicdispersion or ultrahigh-pressure dispersion (ultrahigh-pressurehomogenizer) may be employed if necessary. The concentration of thesmectite dispersion solution is not particularly limited, but it isdesirable to be 1 to 50% by weight so as to maintain stability in thesolution of the metal plate microparticles.

According to the present invention, the dispersion solution may containa resin. Examples of the resin include at least one type selected fromthe group consisting of polyol, polycarboxylic acid, polysulfonic acid,polyether, polyester, polyamide, polyvinyl butyral, polysiloxane,polyvinyl pyrrolidone and polycation compound, which may be used aloneor in a suitable combination.

In Step 2 mentioned above, the method for coating the dispersionsolution onto the support is not particularly limited. For example, aknown method such as gravure coating, reverse coating, roll coating,spray coating, die coating or bar coating may be used for application.

In Step 3 mentioned above, the pressure and the temperature upon thestep of removing the liquid dispersion medium from the coated film mayappropriately be selected according to the smectite, the metal platemicroparticles and the liquid dispersion medium used. For example, ifthe liquid dispersion medium is water, the liquid dispersion medium canbe removed at 25° C. to 60° C. under a normal pressure.

EXAMPLES

Hereinafter, the present invention will be described specifically bymeans of examples, although the present invention is not limited tothese examples. Various improvements and modifications are includedwithout departing from the spirit of the present invention.

Example 1

The main materials used were as follows.

[Silver Nanoparticle Aqueous Dispersion]

As a silver nanoparticle aqueous dispersion, a prototype from Dai NipponToryo was used. This dispersion solution was an aqueous dispersion ofmixed-type silver nanoparticles that contains plate-like particles andpolyhedron particles including spherical particles. The average longaxis of the principal plane of the plate-like microparticles was 500 nmto 800 nm and the thickness thereof was 10 nm to 20 nm. The averageparticle size of the spherical particles was 150 nm. The content ofsilver in the dispersion solution was 0.006% by weight.

[Preparation of Lipophilic Clay-Based Intercalation Compound]

1 gram of synthetic saponite from Kunimine Industries Co., Ltd. (tradename: SA) was dispersed in 60 ml of pure water so as to formmicroparticles, thereby preparing a dispersion solution. A solutionobtained by dissolving 1 gram of benzyloctadecyl dimethyl ammoniumchloride into 60 ml of pure water heated to 50° C. in advance was addedto a microparticle dispersion solution containing the above-describedsaponite, while stirred with heat at 50° C. At the end of mixing,stirring was continued for an hour. Thereafter, the solution was leftovernight and the temperature was allowed to return to room temperature.The resulting precipitated white sediment was filtered, collected,washed with 100 ml of pure water followed by cold methanol and dried.

[Preparation of Silver Nanoparticle-Lipophilic Clay Composite]

1% by weight of toluene dispersion solution of the above-describedlipophilic synthetic clay was prepared. 11 ml of viscous liquid wascollected, diluted with 9 ml of a mixed solvent of dichlorobenzene:chloroform=1:3 (vol/vol), then added and well shaken with 100 ml of theabove-described silver nanoparticle aqueous dispersion. The resultantwas subjected to extracting operation and left alone, which resultedthree separated layers, i.e., a water phase, a bluish-green phase and anocher color phase from the top. The ocher color phase was collected fromthe separated layer, to which a mixed solvent of a large amount of waterand ethanol was added, thereby obtaining beige sediment. This sedimentwas collected, filtered, washed with a large amount of ethanol and thendried. This collected substance was dispersed in a mixed solvent of DMSOand water to obtain a dispersion solution, which was used to form afilm. In a picture of this film taken with a scanning electronmicroscope, plate-like silver nanoparticles embedded in a large amountof fine lipophilic synthetic clay were observed.

Example 1 was assessed according to the following method.

The above-described silver nanoparticle-lipophilic clay composite wasused to prepare a dispersion solution for application that will bedescribed in the following section. The dispersion solution was directlyapplied on the light-receiving surface of the silicon photodiode(S2386-8K from Hamamatsu Photonics) to form a film (dried), and then thephotocurrent resulting from light irradiation was measured with apotentiostat-galvanostat (COMPACTSTAT from Ivium Technologies). In orderto confirm the increase in the photocurrent upon application of thecomposite dispersion solution, the ratio of the photocurrent before andafter the application of the composite (photocurrent after applicationof the composite/photocurrent before application of the composite) wasdetermined with the same silicon photodiode. The light radiated on thesilicon photodiode was the light emitted directly from the Xe lamp asthe light source of HM-25Q hyper monolight from JASCO Corporation whilesetting the wavelength counter to 0 nm.

[Preparation of Silver Nanoparticle-Lipophilic Clay Composite DispersionSolution Used for Application onto Silicon Photodiode]

The sediment (powdery) of the above-described composite of silvernanoparticles and lipophilic clay collected was dispersed in a mixedsolvent of γ-butyrolactone: IPA=1:1 (vol/vol) to form microparticles(first IPA was used for dispersion followed by addition ofγ-butyrolactone and the resultant was subjected to ultrasonic dispersionfor about 30 minutes). The resulting dispersion solution was used anddirectly applied onto the light-receiving surface of the siliconphotodiode to form a film (dried). Then, the photocurrent of the siliconphotodiode was measured according to the above-described technique,confirming an increase in the photocurrent by approximately 4% ascompared to the case before the application.

Comparative Example 1 Preparation of Composition of SilverNanoparticle-Hydrophilic Clay Composite

In the preparation of the composite of silver nanoparticles andlipophilic clay shown in Example 1, hydrophilic synthetic saponite thatwas not substituted with quaternary ammonium (synthetic saponite fromKunimine Industries Co., Ltd., trade name: SA) was directly used,instead of lipophilic synthetic clay, to prepare 1% by weight of anaqueous dispersion. 11 ml was taken from the prepared dispersionsolution, and added with 100 ml of the silver nanoparticle aqueousdispersion described in Example 1 followed by 9 ml of a mixed solvent ofdichlorobenzene: chloroform=1:3 (vol/vol). Thereafter, the solution waswell shaken, subjected to extracting operation and left alone, whichresulted two separated layers, i.e., a grayish black water phase and acolorless transparent organic phase from the top. From the separatedlayers, the grayish black phase was taken and added with a large amountof ethanol to filtrate the sediment. The filtrated sediment was washedwith a large amount of ethanol and then dried.

Next, in the same manner as the preparation of the dispersion solutionof the composite of silver nanoparticles and lipophilic clay forapplication onto a silicon photodiode described in Example 1, thesediment (powdery) of the composite of silver nanoparticles andhydrophilic clay collected as described above was dispersed in a mixedsolvent of γ-butyrolactone: IPA=1:1 (vol/vol) to form microparticles. Asa result, a grayish black dispersion solution was obtained, whichimmediately gave black sediment when left alone, revealing that thedispersion stability as a paint was extremely poor.

Moreover, in the same manner as Example 1, this dispersion solution wasdirectly applied onto the light-receiving surface of the above-describedphotodiode and dried. As a result, agglomerates were occasionallyobserved and did not form a uniform coating. Subsequently, an assessmentmethod similar to that in Example 1 was employed to measure thephotocurrent of the silicon photodiode. As a result, photocurrent thatwas only about 70% of that before the application was obtained, showingno sign of amplification of the photocurrent, unlike Example 1.

Example 2 Preparation of Plate-Like Silver Nanoparticle AqueousDispersion

A plate-like silver nanoparticle aqueous dispersion was prepared in thefollowing procedure (silver content: 0.001% by weight). All of thereagents used were Wako Special Grade from Wako Pure ChemicalIndustries.

(i) 250 μl of a 150 mM trisodium citrate aqueous solution, 50 μl of a 50mM silver nitrate aqueous solution and 60 μl of 30% hydrogen peroxidewater were sequentially added to 24 ml of ultrapure water whilestirring.

(ii) 125 μl of a 100 mM sodium tetrahydroborate aqueous solutionprepared at ice temperature was added while stirring more vigorously.

(iii) Vigorous stirring was continued at least for 30 minutes after theaddition of the sodium tetrahydroborate aqueous solution. The resultantwas left to stand for another five days or longer, thereby obtaining anaqueous dispersion of silver nanoplate nuclei a.

(iv) 1250 μl of the above-described aqueous dispersion of silvernanoplate nuclei a and 65 μl of a 20 mM ascorbic acid aqueous solutionwere sequentially added to 18 ml of ultrapure water while stirring.

(v) 4750 μl of a 0.5 mM silver nitrate aqueous solution was added at aflow rate of 1000 μl/min while stirring more vigorously.

(vi) Immediately after the addition of the above-described silvernitrate aqueous solution, 1000 μl of a 150 mM trisodium citrate aqueoussolution was added and the stirring rate was slowed down. After 4 hoursof continuous stirring, an aqueous dispersion of silver nanoplate nucleib was obtained.

(vii) 1250 μl of the above-described aqueous dispersion of silvernanoplate nuclei b and 78 μl of a 20 mM ascorbic acid aqueous solutionwere sequentially added to 18 ml of ultrapure water while stirring.

(viii) 5700 μl of a 0.5 mM silver nitrate aqueous solution was added ata flow rate of 1000 μl/min while stirring more vigorously.

(ix) At the end of the addition of the above-described silver nitrateaqueous solution, the stirring rate was slowed down, and stirring wascontinued for another 4 hours, thereby obtaining an aqueous dispersionof plate-like silver nanoparticles.

The finally obtained silver nanoplate aqueous dispersion was dried andobserved with SU8000 series scanning electron microscope from Hitachi.As a result, the shapes of the principal planes of the silver nanoplateswere a triangle or a hexagon, where the long axis of the principal planewas 500 nm or longer, the thickness was 10 to 20 nm, and no sphericalsilver nanoparticles were found to be contained (see FIG. 4).

[Preparation of Plate-Like Silver Nanoparticle-Lipophilic ClayComposite]

1% by weight of dichlorobenzene dispersion solution of the lipophilicsynthetic clay described in Example 1 was prepared. Then, 0.1 ml wastaken from the prepared dispersion solution, diluted withdichlorobenzene to 2 ml, then added and well shaken with 100 ml of theabove-described silver nanoplate aqueous dispersion, subjected toextracting operation and left alone, which resulted an organic phasewith a fairly pale light blue color. Since the water phase thatpresented the pale light blue color became completely colorless uponleaving alone, most of the plate-like silver nanoparticles in the waterphase seemed to have moved to the organic phase and condensed uponforming a composite with the lipophilic synthetic clay. The condensationrate numerically reached 100 ml/2 ml=50 times.

Next, a polyvinyl butyral resin was added to this organic phase solutionto 0.005% by weight to obtain a paint material. Subsequently, anequivalent amount of ethanol was added to said material, and theresultant was applied onto a glass substrate that had underwent alkalinewash. The resultant was heat dried with a drier. As a result, a coatinghaving almost colorless and transparent interference fringes was formed,which was confirmed to keep adhesion even upon contact with alcohol.Moreover, the surface resistance of said coating was measured to be at avalue of around 10³ Ω/sq. at normal temperature and pressure, confirmingan effect of significantly increasing conductivity that was higher bysix figures or more than that in the case of glass substrate only.

Comparative Example 2 Preparation of Plate-Like SilverNanoparticle-Hydrophilic Clay Composite

1% by weight of an aqueous dispersion of the hydrophilic syntheticsaponite described in Comparative Example 1 was prepared. 0.1 ml wastaken from the prepared dispersion solution, added with 100 ml of thesilver nanoplate aqueous dispersion described in Example 2, then addedand well shaken with 2 ml of dichlorobenzene, subjected to extractingoperation and left alone, which resulted a colorless and transparentorganic phase, unlike Example 2. The water phase that presented palelight blue color maintained its nature while it was left alone.Accordingly, most of the plate-like silver nanoparticles of the waterphase seemed to have remained in the water phase.

Next, a polyvinyl alcohol resin was added to this water phase solutionto 0.005% by weight to obtain a paint material. Subsequently, anequivalent amount of ethanol was added to this material and theresultant was applied onto a glass substrate that had underwent alkalinewash. The resultant was heat dried with a drier. As a result, anununiform coating with scattering agglomerates was formed. This drycoating easily peeled off from the substrate upon contact with alcohol.Moreover, the surface resistance of said coating was measured to be at avalue of around 10¹⁰ Ω/sq. at normal temperature and pressure, which wasenormously large and cannot be compared with Example 2.

Example 3 Preparation of Naturally-Derived Lipophilic Clay-BasedIntercalation Compound

1 gram of natural montmorillonite (from Kunimine Industries Co., Ltd.,trade name: Kunipia F) was dispersed in 60 ml of pure water inmicroparticles to prepare a dispersion solution. A solution, in which0.5 grams of trimethyl octadecyl dimethyl ammonium chloride wasdissolved in 60 ml of pure water that had been heated to 50° C., wasadded to the above-described microparticle dispersion solutioncontaining the natural montmorillonite while stirring and heating at 50°C. After mixing the solution, an hour of stirring was continued and theresultant was left overnight so that the temperature was allowed toreturn to room temperature. Pale yellow sediment precipitated. Theprecipitated sediment was filtered, collected, washed with 100 ml ofpure water and cold methanol in this order and dried.

[Preparation of Composite of Plate-Like Silver Nanoparticles andNaturally-Derived Lipophilic Clay]

1% by weight of a dichlorobenzene dispersion solution of theabove-described naturally-derived lipophilic synthetic clay wasprepared. 0.1 ml was taken from the prepared dispersion solution,diluted to 2 ml with dichlorobenzene, added and well shaken with 100 mlof silver nano plate aqueous dispersion described in Example 2,subjected to extracting operation and left alone, which resulted anorganic phase with a fairly pale light blue color. Since the water phasethat presented the pale light blue color became completely colorlesswhile being left alone, most of the plate-like silver nanoparticles inthe water phase seemed to have moved to the organic phase and condensedupon forming a composite with the naturally-derived lipophilic clay. Thecondensation rate numerically reached 100 ml/2 ml=50 times.

Next, polyvinyl butyral resin was added to this organic phase solutionto 0.005% by weight to obtain a paint material. Subsequently, anequivalent amount of ethanol was added to said material, and theresultant was applied onto a glass substrate that had underwent alkalinewash. The resultant was heat dried with a drier. As a result, a coatinghaving almost colorless and transparent interference fringes was formed,which was confirmed to keep adhesion even upon contact with alcohol.Moreover, the surface resistance of said coating was measured to be at avalue of around 10³ Ω/sq. at normal temperature and pressure showing alevel comparable to that of Example 2, confirming an effect ofsignificantly increasing conductivity that was higher by six figures ormore than that in the case of glass substrate only.

INDUSTRIAL APPLICABILITY

The structure of the present invention can be formed into a film-likesupport or formed into a film for application to an antistatic film, aconductive film, a transparent conductive film, an antireflective film,a transparent electrode for electronic paper, an antibacterial film, acatalyst carrier film, a light scattering coating film, mother paste, aplasmonic collector film or the like, or can be coated on asemiconductor or the like for application to a flexible solar cell, aphotoelectric converter device such as electroluminescence, an opticalcapacitor, an optical storage battery or the like.

1. A structure comprising metal microparticles and a lipophilicclay-based intercalation compound at a weight ratio of 0.01 to
 50. 2.The structure according to claim 1, wherein the metal microparticles isat least one selected from a group consisting of gold, silver, copper,platinum, palladium and rhodium.
 3. The structure according to claim 1,wherein at least some of the metal microparticles have a plate-likeshape, where the thickness thereof is 1 nm to 50 nm and the long axis ofthe principal plane thereof is 10 nm to 5000 nm.
 4. The structureaccording to claim 3, wherein the aspect ratio of the plate-like metalmicroparticles is 3 or more.
 5. The structure according to claim 1,wherein the metal microparticles contain at least silver.
 6. Thestructure according to claim 1, wherein the lipophilic clay-basedintercalation compound belongs to a lipophilic montmorillonite mineralgroup or mica mineral group.
 7. The structure according to claim 1,wherein the lipophilic clay-based intercalation compound is lipophilicsmectite, lipophilic saponite or lipophilic hectorite.
 8. The structureaccording to claim 7, wherein the lipophilic clay-based intercalationcompound is a synthetic compound.
 9. The structure according to claim 1,which is a film-like structure.
 10. A method for producing a structurecontaining metal microparticles and a lipophilic clay-basedintercalation compound at a weight ratio of 0.01 to 50, the methodcomprising Steps 1 to 3 below: Step 1: step of preparing a dispersionsolution containing metal microparticles, a clay-based intercalationcompound and a liquid dispersion medium such that the weight ratio ofthe metal microparticles and the lipophilic clay-based intercalationcompound is 0.01 to 50; Step 2: step of coating the dispersion solutionon a support to obtain a coated film; and Step 3: step of removing theliquid dispersion medium from the coated film.
 11. The method accordingto claim 10, wherein the dispersion solution in Step 1 contains a resin.12. The method according to 11, wherein the resin is at least one typeselected from the group consisting of polyol, polycarboxylic acid,polysulfonic acid, polyether, polyester, polyamide, polyvinyl butyral,polysiloxane, polyvinyl pyrrolidone and polycation compound.